1. Field of the Invention
The present invention relates to an X-ray image pickup apparatus, more specifically, a large-screen X-ray image pickup apparatus which can carry out actual-size readout with respect to information sources, and a method of making the same.
2. Related Background Art
Since X-ray image pickup apparatus having a large detection area can read out inner information of a specimen by means of an optical system having a power of 1:1 with respect to the specimen, they have been expected for use, for example, in medical fields such as general diagnoses of chest, digestive organs, circulatory organs, and mammography; and their development has remarkably been in progress.
It is ideal for such a large X-ray image pickup apparatus to use a single-plate panel-like semiconductor image sensor having a large area as imaging means for making it possible to capture X-ray images. However, since the yield per sheet of the panel-like semiconductor image sensor decreases as its area becomes larger, sufficient performances and lower cost are hard to achieve at present.
Therefore, a large X-ray image pickup apparatus uses imaging means having a structure in which a plurality of panel-like semiconductor image sensors are arranged side-by-side as being attached to each other like tiles on a base plate made of a hard substrate.
For example, Japanese Patent application Laid-Open No. HEI 9-260626 discloses a photoelectric converter apparatus for an X-ray image pickup apparatus and the like, in which four panel-like semiconductor image sensors are arranged side-by-side as being attached to each other like tiles on a base plate made of a hard substrate.
However, the above-mentioned X-ray image pickup apparatus using a plurality of panel-like semiconductor image sensors has been problematic heretofore in that desirable excellent image resolutions cannot be obtained.
Though one using a soft intensifying screen in place of the base plate made of a hard substrate has also been known, it has been problematic in that it fails to yield a sufficient image resolution whereas its handling in the manufacturing process is unfavorable.
In view of the foregoing problems, it is an object of the present invention to provide an X-ray image pickup apparatus which has a favorable image resolution and can easily be made at a low cost, and a method of making the same.
The X-ray image pickup apparatus in accordance with the present invention is an X-ray image pickup apparatus comprising first and second semiconductor image sensor chips arranged adjacent each other on a base plate, and a scintillator panel disposed on the first and second semiconductor image sensor chips; wherein respective planes including surfaces of photosensitive regions of the first and second semiconductor image sensor chips are intersected at a predetermined angle.
The inventors studied reasons why excellent desirable image resolutions have not been obtained so far in the conventional X-ray image pickup apparatus using a plurality of panel-like semiconductor image sensors, and have found that the warpage occurring in the scintillator panel used for converting the wavelength of X-rays is greatly influential. This warpage is generated by a heat treatment carried out when depositing a fluorescent substance on a surface of X-ray-transparent hard substrate so as to form a fluorescent substance layer in the process of making the scintillator panel. The warpage becomes greater as the area of the scintillator panel is larger.
In the conventional X-ray image pickup apparatus, a plurality of panel-like semiconductor image sensors are disposed so as to face the scintillator panel, while being adjacent each other with their respective photosensitive regions being arranged on a single plane having no steps. Here, since the scintillator panel usually has warpage, a gap occurs between the scintillator panel and each of the photosensitive regions of a plurality of panel-like semiconductor image sensors. Also, when the surface of the scintillator is divided into a plurality of partial areas, and the gap occurring with respect to each of the photosensitive regions of the panel-like semiconductor image sensors is taken into consideration for each partial area, the size of gap greatly fluctuates among a plurality of partial areas, whereby the image resolution greatly deteriorates.
For example, the X-ray image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. HEI 9-260626 tries to improve the image resolution by arranging respective photosensitive regions of four panel-like semiconductor image sensors on a single plane having no steps by adjusting the thickness of the adhesive bonding the four panel-like semiconductor image sensors and the base plate on which they are disposed side-by-side like tiles. In this X-ray image pickup apparatus, a fluorescent substance is directly deposited on the photosensitive regions of the four panel-like semiconductor image sensors, whereby the photosensitive regions are considered to deteriorate due to the heat treatment carried out at the time of evaporation.
Also, a structure using a separate scintillator panel so that the surface of the X-ray fluorescent substance layer is brought into close contact with the photosensitive regions of panel-like semiconductor image sensors does not seem to yield a sufficient image resolution, since it cannot overcome the above-mentioned problem caused by the warpage occurring in the scintillator panel.
In the present invention, by contrast, the surfaces of photosensitive regions of a plurality of semiconductor image sensor chips are not parallel to each other, i.e., the surfaces are intersected at a predetermined angle, whereby the respective photosensitive regions of a plurality of panel-like semiconductor image sensors can attain their optimal arrangement positions in conformity to the curved surface of scintillator panel. Therefore, the fluctuation in gaps between a plurality of partial areas of the curved surface of scintillator panel and the photosensitive regions of semiconductor image sensor chips can be reduced dramatically as compared with that conventionally exhibited. Namely, a plurality of partial areas of the scintillator panel and the respective photosensitive regions of a plurality of semiconductor image sensor chips come into close contact with each other more favorably than in the conventional cases.
This X-ray image pickup apparatus also comprises a buffer member, whereby the contact of the respective photosensitive regions of a plurality of panel-like semiconductor image sensors with the curved surface of the scintillator panel can be held more favorably upon receiving a pressure caused by the buffer member.
The pressure caused by the buffer member can be adjusted to such an extent that the photosensitive regions of the semiconductor image sensor chips and the curved surface of the X-ray fluorescent substance layer of the scintillator panel in contact therewith do not yield such inconveniences as damages and peeling of the fluorescent substance. As a consequence, the X-ray image pickup apparatus of the present invention can attain a favorable resolution and improves the yield.
The magnitude of warpage of the scintillator panel can be measured actually, though it can indirectly be measured by grasping it beforehand upon determining the constituent material of the hard substrate partly constituting the panel and the constituent material of the X-ray fluorescent substance layer and determining the condition for depositing the fluorescent substance. As a consequence, the individual photosensitive regions can successively be made under a fixed arrangement condition, whereby a high productivity can be realized.
In the X-ray image pickup apparatus, the base plate may have an inclined face constituting a bottom part of a case and corresponding to an inclination of a plurality of panel-like semiconductor image sensors. As a consequence, the arrangement of the respective photosensitive regions of a plurality of semiconductor image sensor chips with respect to a plurality of partial areas of the scintillator panel can be adjusted according to the inclination of the surface of support for mounting an imaging unit. The imaging unit is constituted by the semiconductor image sensor chips and image sensor substrates.
For adjusting the extent of warpage, the X-ray image pickup apparatus of the present invention may use a height adjusting part disposed between the bottom part of the case and a plurality of panel-like semiconductor image sensors. This can adjust the arrangement of the respective photosensitive regions of a plurality of semiconductor image sensor chips with respect to a plurality of partial areas of the scintillator panel according to the form, size, and arrangement position of the height adjusting part disposed on the surface of support for mounting the imaging unit.
Also, the X-ray image pickup apparatus of the present invention can carry out adjustment by using an adhesive for bonding the bottom part of the case and a plurality of panel-like semiconductor image sensors. This can adjust the arrangement of the respective photosensitive regions of a plurality of semiconductor image sensor chips with respect to a plurality of partial areas of the scintillator panel according to the amount of supply, thickness, and coating position of the adhesive applied onto the surface of support for mounting the imaging unit.
Further, in the X-ray image pickup apparatus of the present invention, the fluorescent substance may be a needle or columnar crystal vertically growing on a surface of the hard substrate.
Also, in the X-ray image pickup apparatus of the present invention, the hard substrate may be formed from at least one kind of constituent material selected from the group consisting of Al, SiO2, Be, and C.
The manufacturing method of the present invention comprises a first step of measuring an extent of warpage of a scintillator panel; a second step of applying an adhesive onto a base plate; a third step of inclining a plurality of semiconductor image sensor chips according to the extent of warpage and sticking the plurality of semiconductor image sensor chips on the adhesive; a fourth step of disposing the scintillator panel on the plurality of semiconductor image sensor chips; and a fifth step of disposing and pressing a buffer member on the scintillator panel.